四舍五入:四舍五入到第二:

dateTime.AddTicks(-dateTime.Ticks % TimeSpan.TicksPerSecond)

替换为TicksPerMinute以四舍五入到分钟。

如果您的代码对性能敏感，请谨慎处理

new DateTime(date.Year, date.Month, date.Day, date.Hour, date.Minute, date.Second)

我的应用在System.DateTime.GetDatePart中花费了12%的CPU时间。

在我的情况下，我的目标是从datetimePicker工具保存TimeSpan，而不节省秒和毫秒，这里是解决方案。

首先转换datetimePicker。值转换为你想要的格式，我的格式是“HH:mm”，然后将其转换回TimeSpan格式。

var datetime = datetimepicker1.Value.ToString("HH:mm");
TimeSpan timeSpan = Convert.ToDateTime(datetime).TimeOfDay;

2上述解决方案的扩展方法

    public static bool LiesAfterIgnoringMilliseconds(this DateTime theDate, DateTime compareDate, DateTimeKind kind)
    {
        DateTime thisDate = new DateTime(theDate.Year, theDate.Month, theDate.Day, theDate.Hour, theDate.Minute, theDate.Second, kind);
        compareDate = new DateTime(compareDate.Year, compareDate.Month, compareDate.Day, compareDate.Hour, compareDate.Minute, compareDate.Second, kind);

        return thisDate > compareDate;
    }


    public static bool LiesAfterOrEqualsIgnoringMilliseconds(this DateTime theDate, DateTime compareDate, DateTimeKind kind)
    {
        DateTime thisDate = new DateTime(theDate.Year, theDate.Month, theDate.Day, theDate.Hour, theDate.Minute, theDate.Second, kind);
        compareDate = new DateTime(compareDate.Year, compareDate.Month, compareDate.Day, compareDate.Hour, compareDate.Minute, compareDate.Second, kind);

        return thisDate >= compareDate;
    }

用法:

bool liesAfter = myObject.DateProperty.LiesAfterOrEqualsIgnoringMilliseconds(startDateTime, DateTimeKind.Utc);

与其放弃毫秒然后比较，为什么不比较差异呢?

DateTime x; DateTime y;
bool areEqual = (x-y).TotalSeconds == 0;

or

TimeSpan precision = TimeSpan.FromSeconds(1);
bool areEqual = (x-y).Duration() < precision;

下面是一个基于之前答案的扩展方法，它可以让你截断到任何分辨率…

用法:

DateTime myDateSansMilliseconds = myDate.Truncate(TimeSpan.TicksPerSecond);
DateTime myDateSansSeconds = myDate.Truncate(TimeSpan.TicksPerMinute)

类:

public static class DateTimeUtils
{
    /// <summary>
    /// <para>Truncates a DateTime to a specified resolution.</para>
    /// <para>A convenient source for resolution is TimeSpan.TicksPerXXXX constants.</para>
    /// </summary>
    /// <param name="date">The DateTime object to truncate</param>
    /// <param name="resolution">e.g. to round to nearest second, TimeSpan.TicksPerSecond</param>
    /// <returns>Truncated DateTime</returns>
    public static DateTime Truncate(this DateTime date, long resolution)
    {
        return new DateTime(date.Ticks - (date.Ticks % resolution), date.Kind);
    }
}

以下将适用于具有分数毫秒的DateTime，并保留Kind属性(Local, Utc或Undefined)。

DateTime dateTime = ... anything ...
dateTime = new DateTime(
    dateTime.Ticks - (dateTime.Ticks % TimeSpan.TicksPerSecond), 
    dateTime.Kind
    );

或等价的或更短的:

dateTime = dateTime.AddTicks( - (dateTime.Ticks % TimeSpan.TicksPerSecond));

这可以推广为一个扩展方法:

public static DateTime Truncate(this DateTime dateTime, TimeSpan timeSpan)
{
    if (timeSpan == TimeSpan.Zero) return dateTime; // Or could throw an ArgumentException
    if (dateTime == DateTime.MinValue || dateTime == DateTime.MaxValue) return dateTime; // do not modify "guard" values
    return dateTime.AddTicks(-(dateTime.Ticks % timeSpan.Ticks));
}

使用方法如下:

dateTime = dateTime.Truncate(TimeSpan.FromMilliseconds(1)); // Truncate to whole ms
dateTime = dateTime.Truncate(TimeSpan.FromSeconds(1)); // Truncate to whole second
dateTime = dateTime.Truncate(TimeSpan.FromMinutes(1)); // Truncate to whole minute
...